hw/core/machine.c | 3 +++ hw/virtio/virtio-balloon-pci.c | 12 ++++++++++++ 2 files changed, 15 insertions(+)
Most virtio-pci devices allow MSI-X. Add it to virtio-balloon-pci, but
only enable it in new machine types, so we don't break migration of
existing machine types between different qemu versions.
This copies what was done for virtio-rng-pci in:
9ea02e8f1306 ("virtio-rng-pci: Allow setting nvectors, so we can use MSI-X")
bad9c5a5166f ("virtio-rng-pci: fix migration compat for vectors")
62bdb8871512 ("virtio-rng-pci: fix transitional migration compat for vectors")
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
---
v2:
- Remove DEFINE_PROP_END_OF_LIST()
- Declare virtio_balloon_properties as const
hw/core/machine.c | 3 +++
hw/virtio/virtio-balloon-pci.c | 12 ++++++++++++
2 files changed, 15 insertions(+)
diff --git a/hw/core/machine.c b/hw/core/machine.c
index c23b39949649..8f396ef8035a 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -38,6 +38,9 @@
GlobalProperty hw_compat_9_2[] = {
{"arm-cpu", "backcompat-pauth-default-use-qarma5", "true"},
+ { "virtio-balloon-pci", "vectors", "0" },
+ { "virtio-balloon-pci-transitional", "vectors", "0" },
+ { "virtio-balloon-pci-non-transitional", "vectors", "0" },
};
const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);
diff --git a/hw/virtio/virtio-balloon-pci.c b/hw/virtio/virtio-balloon-pci.c
index ce2645ba7187..db7e1cb47537 100644
--- a/hw/virtio/virtio-balloon-pci.c
+++ b/hw/virtio/virtio-balloon-pci.c
@@ -35,11 +35,22 @@ struct VirtIOBalloonPCI {
VirtIOBalloon vdev;
};
+static const Property virtio_balloon_properties[] = {
+ DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
+ VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+ DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
+ DEV_NVECTORS_UNSPECIFIED),
+};
+
static void virtio_balloon_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
{
VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);
DeviceState *vdev = DEVICE(&dev->vdev);
+ if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
+ vpci_dev->nvectors = 2;
+ }
+
vpci_dev->class_code = PCI_CLASS_OTHERS;
qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
}
@@ -55,6 +66,7 @@ static void virtio_balloon_pci_class_init(ObjectClass *klass, void *data)
pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_BALLOON;
pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
pcidev_k->class_id = PCI_CLASS_OTHERS;
+ device_class_set_props(dc, virtio_balloon_properties);
}
static void virtio_balloon_pci_instance_init(Object *obj)
base-commit: 7433709a147706ad7d1956b15669279933d0f82b
--
2.47.1This patch v2 has been successfully tested in s390x. Here the detailed
test steps:
Boot up a VM already containing a memory object
/home/qemu/build/qemu-system-s390x \
...
-m 4G,maxmem=20G \
-object memory-backend-ram,id=mem0,size=16G,reserve=off \
...
Check the virtio-balloon
(qemu) info balloon
Error: No balloon device has been activated
Check the PCI devices in the guest
[root@localhost ~]# lspci -v
[root@localhost ~]#
Hotplug a virtio-balloon-pci device and query it again.
(qemu) device_add virtio-balloon-pci,id=balloon0
(qemu) info balloon
balloon: actual=4096
Deflate the balloon verify the new size
(qemu) balloon 2048
(qemu) info balloon
balloon: actual=2048
Check again the PCI devices in the guest
[root@localhost ~]# lspci -v
0001:00:00.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
Subsystem: Red Hat, Inc. Device 0005
Physical Slot: 00000000
Flags: bus master, fast devsel, latency 0, IOMMU group 0
Memory at 4001000000000000 (32-bit, non-prefetchable) [virtual] [size=4K]
Memory at 4002000000000000 (64-bit, prefetchable) [size=16K]
Capabilities: [98] MSI-X: Enable+ Count=2 Masked-
Capabilities: [84] Vendor Specific Information: VirtIO: <unknown>
Capabilities: [70] Vendor Specific Information: VirtIO: Notify
Capabilities: [60] Vendor Specific Information: VirtIO: DeviceCfg
Capabilities: [50] Vendor Specific Information: VirtIO: ISR
Capabilities: [40] Vendor Specific Information: VirtIO: CommonCfg
Kernel driver in use: virtio-pci
Tested-by: Mario Casquero <mcasquer@redhat.com>
On Wed, Jan 15, 2025 at 5:16 PM Reza Arbab <arbab@linux.ibm.com> wrote:
>
> Most virtio-pci devices allow MSI-X. Add it to virtio-balloon-pci, but
> only enable it in new machine types, so we don't break migration of
> existing machine types between different qemu versions.
>
> This copies what was done for virtio-rng-pci in:
> 9ea02e8f1306 ("virtio-rng-pci: Allow setting nvectors, so we can use MSI-X")
> bad9c5a5166f ("virtio-rng-pci: fix migration compat for vectors")
> 62bdb8871512 ("virtio-rng-pci: fix transitional migration compat for vectors")
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
> ---
> v2:
> - Remove DEFINE_PROP_END_OF_LIST()
> - Declare virtio_balloon_properties as const
>
> hw/core/machine.c | 3 +++
> hw/virtio/virtio-balloon-pci.c | 12 ++++++++++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index c23b39949649..8f396ef8035a 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -38,6 +38,9 @@
>
> GlobalProperty hw_compat_9_2[] = {
> {"arm-cpu", "backcompat-pauth-default-use-qarma5", "true"},
> + { "virtio-balloon-pci", "vectors", "0" },
> + { "virtio-balloon-pci-transitional", "vectors", "0" },
> + { "virtio-balloon-pci-non-transitional", "vectors", "0" },
> };
> const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);
>
> diff --git a/hw/virtio/virtio-balloon-pci.c b/hw/virtio/virtio-balloon-pci.c
> index ce2645ba7187..db7e1cb47537 100644
> --- a/hw/virtio/virtio-balloon-pci.c
> +++ b/hw/virtio/virtio-balloon-pci.c
> @@ -35,11 +35,22 @@ struct VirtIOBalloonPCI {
> VirtIOBalloon vdev;
> };
>
> +static const Property virtio_balloon_properties[] = {
> + DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
> + VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
> + DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
> + DEV_NVECTORS_UNSPECIFIED),
> +};
> +
> static void virtio_balloon_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
> {
> VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);
> DeviceState *vdev = DEVICE(&dev->vdev);
>
> + if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> + vpci_dev->nvectors = 2;
> + }
> +
> vpci_dev->class_code = PCI_CLASS_OTHERS;
> qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
> }
> @@ -55,6 +66,7 @@ static void virtio_balloon_pci_class_init(ObjectClass *klass, void *data)
> pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_BALLOON;
> pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
> pcidev_k->class_id = PCI_CLASS_OTHERS;
> + device_class_set_props(dc, virtio_balloon_properties);
> }
>
> static void virtio_balloon_pci_instance_init(Object *obj)
>
> base-commit: 7433709a147706ad7d1956b15669279933d0f82b
> --
> 2.47.1
>
>
On 15.01.25 17:14, Reza Arbab wrote:
> Most virtio-pci devices allow MSI-X. Add it to virtio-balloon-pci, but
> only enable it in new machine types, so we don't break migration of
> existing machine types between different qemu versions.
>
> This copies what was done for virtio-rng-pci in:
> 9ea02e8f1306 ("virtio-rng-pci: Allow setting nvectors, so we can use MSI-X")
> bad9c5a5166f ("virtio-rng-pci: fix migration compat for vectors")
> 62bdb8871512 ("virtio-rng-pci: fix transitional migration compat for vectors")
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
> ---
This patch enables the virtio-balloon-pci device to be plugged on s390x.
Before this change, plugging that device would fail with "MSI-X support is
mandatory on s390".
However, the device does not seem to be initialized by the Linux guest:
# lspci -v
0001:00:00.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
Subsystem: Red Hat, Inc. Device 0005
Physical Slot: 00000000
Flags: fast devsel, IOMMU group 0
Memory at 4001000000000000 (32-bit, non-prefetchable) [virtual] [size=4K]
Memory at 4002000000000000 (64-bit, prefetchable) [size=16K]
Capabilities: [98] MSI-X: Enable- Count=2 Masked-
Capabilities: [84] Vendor Specific Information: VirtIO: <unknown>
Capabilities: [70] Vendor Specific Information: VirtIO: Notify
Capabilities: [60] Vendor Specific Information: VirtIO: DeviceCfg
Capabilities: [50] Vendor Specific Information: VirtIO: ISR
Capabilities: [40] Vendor Specific Information: VirtIO: CommonCfg
I tried enabling it:
[ 343.718529] pci 0001:00:00.0: enabling device (0000 -> 0002)
Without any change. @s390x folks, is there something missing to make it fly,
or are there additional steps to initialize+use such devices from inside the VM?
--
Cheers,
David / dhildenb
On 27.01.25 14:11, David Hildenbrand wrote:
> On 15.01.25 17:14, Reza Arbab wrote:
>> Most virtio-pci devices allow MSI-X. Add it to virtio-balloon-pci, but
>> only enable it in new machine types, so we don't break migration of
>> existing machine types between different qemu versions.
>>
>> This copies what was done for virtio-rng-pci in:
>> 9ea02e8f1306 ("virtio-rng-pci: Allow setting nvectors, so we can use MSI-X")
>> bad9c5a5166f ("virtio-rng-pci: fix migration compat for vectors")
>> 62bdb8871512 ("virtio-rng-pci: fix transitional migration compat for vectors")
>>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
>> ---
>
> This patch enables the virtio-balloon-pci device to be plugged on s390x.
> Before this change, plugging that device would fail with "MSI-X support is
> mandatory on s390".
>
> However, the device does not seem to be initialized by the Linux guest:
>
> # lspci -v
> 0001:00:00.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
> Subsystem: Red Hat, Inc. Device 0005
> Physical Slot: 00000000
> Flags: fast devsel, IOMMU group 0
> Memory at 4001000000000000 (32-bit, non-prefetchable) [virtual] [size=4K]
> Memory at 4002000000000000 (64-bit, prefetchable) [size=16K]
> Capabilities: [98] MSI-X: Enable- Count=2 Masked-
> Capabilities: [84] Vendor Specific Information: VirtIO: <unknown>
> Capabilities: [70] Vendor Specific Information: VirtIO: Notify
> Capabilities: [60] Vendor Specific Information: VirtIO: DeviceCfg
> Capabilities: [50] Vendor Specific Information: VirtIO: ISR
> Capabilities: [40] Vendor Specific Information: VirtIO: CommonCfg
>
>
> I tried enabling it:
>
> [ 343.718529] pci 0001:00:00.0: enabling device (0000 -> 0002)
>
> Without any change. @s390x folks, is there something missing to make it fly,
> or are there additional steps to initialize+use such devices from inside the VM?
>
Ah! might just be
# CONFIG_VIRTIO_PCI is not set
in my Fedora config,
With that enabled, I think it's working.
--
Cheers,
David / dhildenb
© 2016 - 2026 Red Hat, Inc.